Magnets



bec.` s1, 1963 J. s. Kom/EL 3,116,182

MAGNETS Filed May 29, 1961 Fig. Fig. 2.

// *MMX James S KOU 9/7 by @Mad United States hee 3,116,182 MAGNETS James S. Konvel, Albany, N.Y., assigner to General Electric Company, a corporation of New York Filed May 29, 1961, Ser. No. 113,411 4 Claims. (Cl. 14S-31.57)

This invention relates to magnets and more particularly to magnets having one easy direction of magnetization and to a method for producing such magnets.

Previously known magnetic materials have been most readily magnetized along one or more axes and have been equally readily magnetizable in either direction along each axis. The magnetic properties of these materials have been measured and evaluated by several methods, perhaps the best known being the graphical representation of the hysteresis loop obtained when a magnetic Ifield is applied to the magnetic material in such a manner as to cyclically reverse polarity. Since magnetic properties have been symmetrically reversible, both quantitatively and qualitatively with respect to the axis of magnetization, the magnets have at least two stable positions in a strong magnetic ield.

While existing magnetic materials have generally proven acceptable for use in most situations, the increasing use of electronic and electrical apparatus under unusual environmental conditions has resulted in a need for components having particular properties when subjected to such unusual conditions. For example, various parts of guidance or computer systems must be able to perform reliably at extreme temperatures. Development of these and other technological areas has resulted in recognition that a magnetic material having one easy `direction of magnetization would be of value, particularly where this property could be utilized at low ternperatures.

A principal object of this invention is to provide magnets having one easy direction of magnetization.

Another object of this invention is to provide an alloy magnet consisting essentially of manganese alloyed with a metal from the group of copper, silver and gold which has one easy direction of magnetization.

An additional object of this invention is to provide aA process for producing magnets having one easy direction of magnetization.

Other objects and advantages of this invention will be in part obvious and in part explained by reference to the accompanying speciiication and drawings.

In the drawings:

FIGURE l shows a hysteresis loop illustrating the magnetic characteristics of the usual type permanent magnet;

FIGURE 2 shows a hysteresis loop illustrating the magnetic -characteristics of a copper-manganese magnet made according to the present invention;

FIGURE 3 shows a hysteresis loop illustrating the magnetic characteristics of a silver-manganese magnet made according to the present invention; and

FIGURE 4 is a hysteresis loop illustrating the magnetic properties of a magnet constructed of the same alloy used for FIG. 2 but which was not subjected to a magnetic iield during cooling.

Generally, this invention concerns permanent magnets and a process for producing permanent magnets having one easy direction of magnetization, which magnets comprise bodies containing from about 5 to 30 atomic percent manganese, balance substantially all a metal selected `from the group consisting of copper, silver and gold. The process for producing these magnets generally comprises preparing a suitable alloy body and cooling the alloy body in a magnetic iield to a temperature suiiiciently low t0 create the one easy direction of magnetization, generally K. or less.

`It has been mentioned previously that existing alloy magnets have at least two easy directions of magnetization and also have two equivalent stable positions in an applied magnetic lield.

The hysteresis loop 10 characteristic of the usual type ermanent magnets is shown in FIG. 1, in which the magnetizing eld H, in oersteds, is the axis of the abscissa and the magnetization or M, in e.m.u. is the axis of the ordinate. As the eld is increased from zero to higher values of H in what for convenience may be referred to as the positive direction, the magnetization (M) of the material reaches a maximum value -l-Mmax, for a given eld. If the held -|-H is removed, the value of the magnetization decreases along the demagnetization curve 11 to MR1. If then a -eld -H of reverse polarity is applied, the magnetization of the material continues to decrease along curve 11 and crosses the H axis at the value HC1, the magnetization linally reaching -Mmax as the iield is further increased in the negative direction. If the negative lield is removed, the magnetization of the material correspondingly drops to MR2, which is numerically equal to MRI. Application of the positive ltield then causes the magnetization to move along the magnetization curve 12 and cross the H axis at the value -l-Hc2, which is numerically equal to HC1. As the positive lield is increased, the magnetization of the material rises to the value \-{-Mm,x. The magnetization values M which were used in the present case in place of the flux density, B, to plot the hysteresis loops, are equal to the ux density (B) minus the magnetizing iield (H), divided by 4 pi, as indicated by the formula:

Alloys which can be used, as previously mentioned, to produce magnets having one easy direction of magnetization consist essentially of copper or silver or gold alloyed with from 5 to 30 atomic percent manganese. The copper-manganese alloys will generally contain from 5 to 30 atomic percent manganese, balance substantially all copper, whereas the silver and gold percentages will generally fall within the range of from 15 to 25 atomic percent, balance substantially all manganese.

FIGURE 2 of the drawings shows a hysteresis loop 15 which is characteristic of the magnets of the present invention. The composition of lthe magnet used to produce loop 15 was 24.1 atomic percent manganese, balance copper. Here the loop is shifted toward the negative direction of eld, the material thus being more easily magnetized in the positive direction. The maximum elds Hmm and -l-Hmaxare quantitatively the same, about 10,00() oresteds, but the magnetization values MRI and MR2 are both positive and the -fleld strength HC1 and Hc2 are both negative. It will be noted that the lloop is extremely thin, so that the field and magnetization values are essentially the same, viz., 4,0010 oresteds and 7.5 e.m.u., respectively. Since the two values for MR have the same sign (and magnitude), the material in zero iield is magnetized in the same direction, regardless of the direction of any eld previously impressed on it.

Curve 16, FIGURE 3, illustrates the magnetic properties of a magnet having the composition 23.7 perecent manganese, balance substantially all silver. Once again the magnetization values are both positive, about 7 e.m.u., and ythe field strengths both negative, about 3,750 oersteds.

Examples of several alloys which can be processed to develop the desired properties follow. Only one value is listed for MR and HC, since the magnetizations were both positive and about the same and the iield strengths were both negative and about the same.

:Since the gold-manganese alloys exhibit hysteresis loops which cannot be characterized by single values of MR and Hc, sample compositions of these alloys are set forth in Table II, together with their magnetic properties.

Table 1I Alloy Approx. Temp. him lWRg T101 H02 VllClO Mn, Au, (e.n1.u.) (e.rn.u (oer.) (oer.) Il li'eet Atomic Atomic Disappears, percent percent K.

As has already been stated, the treatment to which the alloys must be subjected is important in achieving magnets having the magnetic properties evidenced by the shifted hysteresis loops. It is felt `that both atomic and magnetic heterogeneity must exist to develop the one easy direction of magnetization, that is, some degree of disorder should exist to bring about the shifted hysteresis loop characteristic, although complete disorder is probably not essential as some residual order may exist in 'almost all systems.

As generally understood, a disordered solid solution alloy is one in which the atoms of the various constituent metals of an alloy are randomly distributed through the alloy lattice. Conversely, an ordered solid solution alloy lis one in which the .atoms of the different metals repeat in lattice position according to a definite pattern.

Broadly, the process involves preparing `a magnet body of a suitable alloy such as one of those previously disclosed, quenching the body from an elevated temperature to retain some `degree of atomic disorder and cooling the body in a magnetic iield to below the temperature vat which the shifted hysteresis loop effect appears. The magnet which results has one easy direction of magnetization.

In order to obtain optimum properties, the field should be maintained down to 'the lowest temperature to which lthe body is cooled. It is felt that the present magnets, as processed, acquire their unique behavior by virtue of ferromagnetic and antiferromagnetic regions present within the body. The coupling effect between the ferromagnetic and the antiferromagnetic regions causes the one easy direction of magnetization. Therefore, during cooling of the body, it is essential that it be subjected to a magnetic field, one on the order of 5,000 oersteds normally being sufiicient to properly align the antiferromagnetic as well as the ferromagnetic moments in any of the alloys. Of course, lesser fields can be used in some cases and still obtain maximum alignment of the magnetic moments within the magnet. Although the magnetic field need only be applied from just above that temperature in which the shifted loop effect begins, as a matter of expedience, it is normally easier to apply the field continuously during the entire cooling treatment.

The effect of cooling the body from room temperature to below the critical temperature Without using a magnetic field can be seen by referring to the loop 20 of FIGURE 4 of ythe drawings. This loop was obtained from the same material used to obtain curve 15 in BIG- URE 2, the difference resulting from :the absence of an applied magnetic field during cooling. The symmetry of the loop with respect to the oiigin clearly indicates that the magnetic field is necessary during cool-ing to obtain the preferred direction of magnetization in the magnets.

Although the present invention has been described in connection with preferred embodiments, it is to be understood that modifications and variations may be restored to without departing from `the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and the appended claims.

What I claim as new and desire to secured by Letters Patent of the United States is:

1. A magnet having one ea'sy direction of magnetization, said magnet being composed of magnetically coupled ferromagnetic and antiferromagnetic regions and compositionally consisting of a solid solution alloy which has at least partial atomic disorder and consists of from about 5 to 30 atomic percent manganese, balance substantially all a metal selected from the group consisting of copper, silver, and gold.

2. A magnet as defined in claim 1 wherein`said solid solution alloy consists essentially of from about 5 to 30 atomic percent manganese, balance substantially all copper.

3. A magnet as defined in claim l wherein said solid solution alloy consists essentially of from about 10 to 25 atomic percent manganese, balance substantially all silver.

4. A magnet as defined in claim 1 wherein said solid solution alloy consists essentially of from about 10 to 25 atomic percent manganese, balance substantially all gold.

References Cited in the file of this patent UNITED STATES PATENTS 2,141,113 Peterson Dec. 20, 1938 2,161,253 Hensel et al. lune 6, 1939 2,161,574 Hensel et al. June 6, 1939 2,298,261 Mittendorf et al Oct. 6, 1942 2,466,202 Brenner Apr. 5, 1949 2,961,360 Kouvel et al Nov. 22, 1960 

1. A MAGNET HAVING ONE EASY DIRECTION OF MAGNETIZATION, SAID MAGNET BEING COMPOSED OF MAGNETICALLY COUPLED FERROMAGNETIC AND ANTIFREEOMAGNETIC REGIONS AND COMPOSITIONALLY CONSISTING OF A SOLID SOLUTION ALLOY WHICH HAS AT LEAST PARTIAL ATOMIC DISORDER AND CONSISTS OF FROM ABOUT 5 TO 30 ATOMIC PERCENT MANGANESE, BALANCE SUBSTANTIALLY ALL A METAL SELECTED GROUP CONSISTING OF COPPER, SILVER AND GOLD. 